ICMCS Seminar - From local to global: magnetic buoyancy and rotational instabilities in the solar tachocline

The tachocline is a thin, stably stratified shear layer in the Sun where large-scale magnetic field is thought to be stored and amplified as part of the solar dynamo. Decades of theory predict several candidate instabilities there, most prominently magnetic buoyancy and rotational instabilities, but much of our existing intuition comes from local or asymptotic analyses. In this talk I will present our recent work, which extends the local stability model of Gilman (2018) to a global spherical-shell geometry and includes viscous and magnetic diffusion.

Using a minimal magnetohydrodynamic (MHD) model with solar-like differential rotation and imposed toroidal magnetic fields, we solve the resulting linear stability problem numerically. We show that the principal instability mechanisms identified in the local theory persist in global geometry in the presence of diffusion, with growth rates and preferred latitudes that closely match local predictions. The global calculation, however, reveals pronounced spatial localisation in latitude and radius. These results provide a firm basis for interpreting how latitude-dependent shear and magnetic structure regulate where the tachocline is prone to instability, and they set the stage for future nonlinear simulations to study saturation and turbulent transport.

Throughout the talk, I will introduce essential MHD concepts as needed. Instabilities will be explained using simple fluid-parcel thought experiments and physics-based analogies.

https://ed-ac-uk.zoom.us/j/81211470751

Meeting ID: 812 1147 0751
Passcode: ICMCS123